The present invention relates to a propelling transmission system of a tractor comprising a main clutch case connected to a rear face of an engine, both mounted at a front position of the tractor, a rear transmission mounted at a rear position of the tractor for receiving drive from a main clutch and outputting the drive to front and rear wheels, and a front wheel change speed mechanism mounted on a transmission line extending from the rear transmission to the front wheels, the front wheel change speed mechanism being switchable between a standard drive mode for driving the front wheels at substantially the same speed as the rear wheels and a high speed mode for driving the front wheels at a higher speed than the rear wheels.
Conventionally, this type of propelling transmission system has the front wheel change speed mechanism disposed at a lower forward position of the rear transmission mounted at the rear position of the tractor as disclosed in U.S. Pat. No. 4,574,910.
The front wheel change speed mechanism is thus disposed at or adjacent the rear position of the tractor. Consequently, the center of gravity of the tractor is biased to the rear of the tractor, which adds to the tendency for the center of gravity to be already in the rear with a working implement such as a plow attached to the rear of the tractor. This situation requires a very heavy balancing weight to be mounted at the front of the tractor.